Polar modulation without analog filtering
View Patent ↗This disclosure relates to systems and methods for polar modulation without analog filters. Digitals filters, a second order hold interpolator and a reconfigurable third order noise shaper can be used instead of the analog filters used in conventional polar modulators. The polar modulator receives either receives the input in polar coordinates or converts the signal into polar phase and amplitude components. The phase and amplitude components are processed separately using digital signal processing components including digital filters, PLL, interpolator and noise shaper. The processed phase and amplitude components are then mixed to generate the modulated signal.
1. A polar modulator without an analog filter, comprising:
an interpolator that upsamples and interpolates a digital amplitude signal;
a noise shaper that reshapes a frequency contour of a quantization noise of the upsampled and interpolated digital amplitude signal, wherein the noise shaper has a first order behavior at DC and a second order behavior at an adjustable frequency offset;
a digital-to-analog converter that converts the reshaped amplitude signal to an analog signal; and
a modulator that combines a phase signal and the analog amplitude signal, and outputs a modulated signal.
2. The polar modulator of claim 1 , wherein the interpolator performs quadratic interpolation while upsampling to a higher sampling rate.
3. The polar modulator of claim 1 , wherein the noise shaper is adaptively adjusted in respect to a transmit frequency.
4. The polar modulator of claim 1 further comprising one or more digital filters to limit spectra of one of the following: the analog amplitude signal, the phase signal, or both.
5. The polar modulator of claim 1 further comprising a differentiator that differentiates the phase signal into a frequency signal proportional to the phase signal.
6. The polar modulator of claim 5 further comprising a phase lock loop that receives the frequency signal and generates a phase-modulated signal at a transmit frequency.
7. The polar modulator of claim 1 further comprising a digital gain control component that amplifies or attenuates the amplitude signal.
8. The polar modulator of claim 7 , wherein digital gain control is applied before the noise shaper.
9. The polar modulator of claim 8 , wherein digital gain control is applied before and after the interpolator.
10. A device implementing a polar modulator without an analog filter, comprising:
a component that provides digital signals, wherein an input signal to the digital signals is either in polar coordinates or is being converted into a polar amplitude signal and a phase signal, and modulates the polar amplitude and the phase signal to a transmit signal; and
a power amplifier that receives the transmit, wherein the polar modulator comprises a third order noise shaper that receives the amplitude signal at an increased sampling rate, and reshapes the frequency contour of the noise of the amplitude signal, and the noise shaping function has a first order behavior at DC and a second order behavior at an adjustable frequency offset.
11. The device of claim 10 , wherein the polar modulator comprises one or more digital filters to process the phase signal and the amplitude signal.
12. The device of claim 10 , wherein the polar modulator comprises a differentiator that differentiates the phase signal into a frequency signal proportional to the phase signal.
13. The device of claim 10 , wherein the polar modulator comprises a second order hold interpolator that increases the sampling rate of the amplitude signal.
14. The device of claim 10 , wherein the noise shaping function is adaptively adjusted in respect to the transmit frequency.
15. The device of claim 10 , wherein the polar modulator comprises digital gain control.
16. The device of claim 15 , wherein the digital gain control is placed before and after the interpolator.
17. The device of claim 10 , wherein the component is one of the following: a baseband unit or an analog to digital converter.
18. A method of implementing polar modulation without an analog filter comprising:
upsampling and interpolating a digital amplitude signal;
reshaping a frequency contour of a quantization noise of the upsampled and interpolated digital amplitude signal, wherein the reshaping has a first order behavior at DC and a second order behavior at an adjustable frequency offset;
converting the reshaped amplitude signal to an analog signal;
combining a phase signal and the analog amplitude signal;
outputting a modulated signal.
19. The method of claim 18 , wherein the upsampling performs quadratic interpolation while upsampling to a higher sampling rate.
20. The method of claim 18 , wherein the reshaping is adaptively adjusted to a transmit frequency.
21. The method of claim 18 further comprising amplifying or attenuating the amplitude signal.